As part of The Great Tagging Survey, I've noticed that the pluralisation of our tags is a bit inconsistent. The following lists all tags that refer to some kind of object that is dealt with in the corresponding challenges.
This is probably not a huge deal, but I think it would be nicer if this was consistent. I don't know if devs can rename tags (although I think they can since they can also delete them), but maybe we want to at least set up a guideline for future tags?
I'll add a few answers, please vote according to your preference or add your own answer.